Re: [PATCH 2/2] clk: Move init fields from clk to clk_hw

From: Turquette, Mike
Date: Tue Mar 27 2012 - 14:49:57 EST

On Mon, Mar 26, 2012 at 9:35 PM, Saravana Kannan <skannan@xxxxxxxxxxxxxx> wrote:
> Mike,
> (*nudge*) (*nudge*)

Hi Saravana,

I spent some time mulling over the ideas this weekend and I agree that
we have 3 types of data, so having the three structs makes some sense.
I'm checking this patch out more earnestly today.


> -Saravana
> On 03/20/2012 08:01 PM, Saravana Kannan wrote:
>> On 03/20/2012 06:47 PM, Turquette, Mike wrote:
>>> On Tue, Mar 20, 2012 at 4:12 PM, Sascha Hauer<s.hauer@xxxxxxxxxxxxxx>
>>> wrote:
>>>> On Tue, Mar 20, 2012 at 01:06:34PM -0700, Saravana Kannan wrote:
>>>>> On 03/20/2012 11:10 AM, Sascha Hauer wrote:
>>>>>> On Tue, Mar 20, 2012 at 10:18:14PM +0800, Shawn Guo wrote:
>>>>>>> On Tue, Mar 20, 2012 at 10:40:31AM +0100, Sascha Hauer wrote:
>>>>>>> ...
>>>>>>>> I am using these functions and don't need a static array, I just
>>>>>>>> call
>>>>>>>> the functions with the desired parameters.
>>>>>>> With this patch getting in, you do not have to use them then. I feel
>>>>>>> a static array will be much more readable than a long list of
>>>>>>> function
>>>>>>> calls with a long list of hardcoded arguments to each.
>>>>>> I'm also not a fan of long argument lists; a divider like defined
>>>>>> in my
>>>>>> tree takes 5 arguments, a gate 4 and a mux 6. While 6 is already at
>>>>>> the
>>>>>> border I think it's still acceptable.
>>>>>> What I like in terms of readability is one line per clock which makes
>>>>>> for quite short clock files.
>>>>> It certainly makes for short clock files, but it's definitely less
>>>>> readable that the expanded struct. For the original author the "one
>>>>> line per clock" looks readable since they wrote it. But for someone
>>>>> looking at the code to modify it, the expanded one would be much
>>>>> easier to read. Also, you can always declare your own macro if you
>>>>> really want to follow the one line approach.
>>>>>> So when we use structs to initialize the clocks we'll probably have
>>>>>> something like this:
>>>>>> static struct clk_divider somediv = {
>>>>>> .reg = CCM_BASE + 0x14,
>>>>>> .width = 3,
>>>>>> .shift = 17,
>>>>>> .lock =&ccm_lock,
>>>>>> .hw.parent = "someotherdiv",
>>>>>> .hw.flags = CLK_SET_RATE_PARENT,
>>>>>> };
>>>>> Taken from your patches:
>>>>> imx_clk_mux("spll_sel", CCM_CSCR, 17, 1, spll_sel_clks,
>>>>> ARRAY_SIZE(spll_sel_clks));
>>>>> Compare the struct to the one line call. Now tell me, what does "1"
>>>>> represent? No clue. But in the struct, I can immediately tell what
>>>>> each one of the parameters are.
>>>>> Anyway, my patch certainly isn't forcing you to use multiple lines.
>>>>> So, hopefully this won't be a point of contention.
>>>>>> This will make a 4000 line file out of a 500 line file. Now when for
>>>>>> some reason struct clk_divider changes we end with big patches. If the
>>>>>> clk core gets a new fancy CLK_ flag which we want to have then again
>>>>>> we end up with big patches. Then there's also the possibility that
>>>>>> someone finds out that .lock and .hw.flags are common to all dividers
>>>>>> and comes up with a #define DEFINE_CLK_DIVIDER again to share common
>>>>>> fields.
>>>>> This patch won't prevent you from doing any of that. You can still
>>>>> create macros for that (there are already one for that). Also, what
>>>>> you are pointing out is a bigger problem for the current
>>>>> clk_register() function since you might have to change the no. of
>>>>> params of all the callers even if a new field is optional.
>>>>>> All this can be solved when we introduce a small wrapper function and
>>>>>> use it in the clock files:
>>>>>> static inline struct clk *imx_clk_divider(const char *name, const
>>>>>> char *parent,
>>>>>> void __iomem *reg, u8 shift, u8 width)
>>>>>> {
>>>>>> return clk_register_divider(NULL, name, parent, CLK_SET_RATE_PARENT,
>>>>>> reg, shift, width, 0,&imx_ccm_lock);
>>>>>> }
>>>>>> It decouples us from the structs used by the clock framework, we can
>>>>>> add our preferred flags and still can share common fields like the
>>>>>> lock.
>>>>>> While this was not the intention when I first converted from struct
>>>>>> initializers to function initializers I am confident that it will make
>>>>>> a good job.
>>>>> Now I'm confused -- it's not clear if you are leaning towards my
>>>>> patch or away from it?
>>>> There was a tendency to get rid of static initializers and I like the
>>>> idea of not exposing any of the internally used members outside the
>>>> clock framework.
>>> I'm with Sascha on this. I feel that dividing the interface strictly
>>> into two halves is the best way.
>> I addressed this concern in my earlier comments. We can make a copy or
>> we can agree the fields I moved to clk_hw aren't really useful wrt
>> writing hacky code and call it a day. Can you please clarify why neither
>> of these options are acceptable?
>>> I have an uneasy feeling about
>>> exposing this stuff into struct clk_hw (or clk_initializer or
>>> whatever). This stretches the data out across three structures and
>>> just doesn't feel right to me.
>> Wrt this discussion, there are three distinct classes of data:
>> 1) Those specific to the platform driver that the common code shouldn't
>> care about.
>> 2) Those specific to the common code that the platform driver shouldn't
>> care about.
>> 3) Stuff that's shared/passed between common code and the platform driver.
>> When we have three classes of data, I don't what's wrong with having
>> three struct types to contain them. If anything, it's better than the
>> current approach of exposing the common clock code specific data (struct
>> clk) to code outside of common clock code just because we want to allow
>> static initialization. The end goal should be to move struct clk inside
>> clk.c.
>> I think this patch just takes us one step close to that since IMX and
>> MSM won't have to include clk-private.h in any of our platform specific
>> files while also allowing OMAP to include it for the near term.
>>>> Now people try their best to make themselves comfortable with the
>>>> static initializers and you even discussed the possibility of removing
>>>> the clk_register_* functions (which make it possible for users not
>>>> to use any of the internal struct members). That's what I don't like
>>>> about your patches. But if we go for static initializers anyway then
>>>> your
>>>> patches probably change things for the better.
>>> Static initialization is something I have fought for; in fact the
>>> original patches provided no way to do it, so clearly what we have
>>> today is some progress for the folks desiring static init.
>> I too desire static init. Sorry if I was unclear and gave people the
>> misconception that I wanted to remove static init.
>>> The patch
>>> above doesn't actually prevent allocation from happening as it still
>>> must call into clk_register and kmalloc struct clk,
>> Correct.
>>> so besides
>>> readability, I'm not sure what these patches buy us.
>> I think readability is very important and if this buys us nothing but
>> readability, we should still take this patch. But there are other
>> benefits too -- I mentioned them in the commit text.
>>> Assuming that C99 designated initializers (for the sole purpose of
>>> readability) is the main draw of the above patch, please let me know
>>> what you think about modifying the existing static init macros so that
>>> your clock data looks like this:
>>> DEFINE_CLK_DIVIDER(dpll_iva_m5x2_ck,&dpll_iva_x2_ck, "dpll_iva_x2_ck",
>>> .flags = 0x0,
>>> .reg = OMAP4430_CM_DIV_M5_DPLL_IVA,
>>> .lock = NULL
>>> );
>>> Note that the first argument is the name of this clock (and will be
>>> properly stringified for .name = "whatever") and that the second and
>>> third arguments are both the parent clock, used for initializing the
>>> parent pointer and .parent_names, respectively. If that aspect of the
>>> macro is too ugly then those can even be broken out into a separate
>>> macro since they are independent data structure (struct clk **parents,
>>> and char **parent_names). Or you could just open code those data
>>> structures and only use a macro for struct clk and struct clk_foo.
>>> This gives you the readability of C99 designated initializers while
>>> keeping struct clk's members totally hidden from the rest of the
>>> world.
>> But it still leaves the struct clk exposed to people who do static init
>> of the clock tree. I think agreeing that the name, parent names, flags
>> and ops are not used to hack with or just making a copy of all of them
>> (and mark the originals as __init if that's doable). is a better
>> solution than trying to go with macros and leave struct clk exposed to
>> everyone who want to do static init of the clock tree.
>> At a later point when we are ready to move struct clk inside clk.c, with
>> this patch applied right now, IMX and MSM won't have to churn their code.
>> Thanks,
>> Saravana
> --
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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